(1) Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device, in particular to a manufacturing method for a III group nitride semiconductor device having heterojunction, such as a light emitting diode (hereafter referred to as LED) in a visible range to an ultraviolet range, a semiconductor laser in a visible range to an ultraviolet range, or a high-speed transistor, and relates to a semiconductor device and a semiconductor wafer manufactured by the III group nitride semiconductor having the heterojunction.
(2) Description of the Related Art
The III group nitride semiconductor made of GaN, InN, AlN or an alloy composed predominantly of these materials is a semiconductor material that can form a hetero-structure of a wide band-gap having an energy gap corresponding to a wave range from a visible light to an ultraviolet radiation. Therefore, it is a preferred material for a LED, a semiconductor laser, a high-speed transistor which can operate in a high temperature environment, and the like.
The III group nitride semiconductor using such as GaN is often grown on a substrate made of different materials such as sapphire and SiC. Therefore, a distortion is generated when it grows because of differences of a grating constant and a thermal expansion coefficient between the substrate and a III group nitride growth layer. Or, when the hetero-structure made of AlGaN or InGaN is formed on GaN, the grating constant and the thermal expansion coefficient are different among GaN, AlGaN and InGaN so that a distortion is generated at the time of the growth. When such distortion is deposited and a limit is reached, a crack is generated on the growth layer. Accordingly, various counter-measurements are taken.
For example, Japanese Laid-Open Patent Publication application No. H11-74621 (related art 1) discloses a technology of moderating a distortion using InGaN for one of the layers which forms a light confinement hetero-structure. The other, Japanese Laid-Open Patent Publication application No. 2002-9341 (related art 2) discloses a technology of moderating a distortion by forming a III group nitride layer on a p-GaN having concavo-convexes.
According to the method, it is possible to thicken a thickness of the growth layer by moderating the distortion and to grow a growth layer which even has a large compositional difference with the base without generating a crack.
However, with the conventional structure, the distortion can be reduced but the crack is propagated to a semiconductor device and a semiconductor substrate when the growth layer grows as much as causing a distortion larger than a destruction limit. Also, there is a limitation for a combination of the base and the growth layer.
Furthermore, in the case where a semiconductor material with a film hetero-structure using InGaN is applied to a light-emitting device with a short wavelength such as a purple light to an ultraviolet radiation, an InGaN layer works as a light absorption layer so that a light-emitting efficiency remarkably declines and an high-efficient semiconductor device cannot be acquired. Further, by a method of forming concavo-convexes on p-GaN which has a base structure, the p-GaN which has an electrical conductivity is used for a base layer so that, when the method is applied to a high-speed transistor, a maximum operation frequency is declined.